Commercially available ion implantation systems employ an ion source that includes a source chamber spaced from an ion implantation chamber where one or more workpieces are treated by ions from the source. An exit opening in the source chamber allows ions to exit the source so they can be shaped, analyzed, and accelerated to form an ion beam. The ion beam is directed along an evacuated beam path to the ion implantation chamber where the ion beam strikes one or more workpieces, typically generally circular wafers. The energy of the ion beam is sufficient to cause ions which strike the wafers to penetrate those wafers in the implantation chamber. In a typical application of such a system the wafers are silicon wafers and the ions are used to "dope" the wafers to create a semiconductor material. Selective implantation with the use of masks and passivation layers allows an integrated circuit to be fabricated.
U.S. Pat. No. 4,764,394 to Conrad entitled "Method and Apparatus for Plasma Source Ion Implantation" discloses an ion implantation system for treating a target by means of ionic bombardment. Ion implantation into surfaces of a three dimensional target is achieved by forming an ionized plasma about the target within an enclosing chamber. Once the plasma is set up in a region surrounding the target, ions from the plasma are driven into the target object from all sides without need to manipulate the target. This implantation is accomplished by application of repetitive pulses of high voltage, typically 20 kilovolts or higher, that cause the ions to be driven into the exposed surfaces of the target. A technique discussed in the '394 patent for setting up the plasma is to introduce a neutral gas into the region of the target and then ionize the gas with ionizing radiation.
The system disclosed in the '394 patent to Conrad uses an ion source to create an ion plasma in a region surrounding a workpiece and then selectively pulses an electrode that supports the workpiece thereby attracting the positive ions in the plasma toward the workpiece.
U.S. Pat. No. 5,654,043 to Shao et al also concerns a system for treating a workpiece surface by causing ions to impact the workpiece surface. A gas is injected into an implantation chamber so that an ionizable gas occupies a region in close proximity to the workpiece surface. A plasma of implantation material is created within the interior region of the implantation chamber by repeatedly relatively biasing conductive electrodes with a sequence of pulses that both ionize the gas molecules injected into the chamber and accelerate the ionized gas molecules toward the implantation surfaces of the one or more workpieces. The disclosure of the '043 patent to Shao et al is incorporated herein by reference.
U.S. Pat. No. 5,658,423 to Angell et al concerns a method of monitoring the status of a plasma in a chamber while conducting an etch process. Spectral analysis data is collected during etching, with the spectral data characterizing an emission of light from an etch species contained in the plasma.
A paper entitled "Dosimetry Measurement in Ion Implanters" copyright 1981 by Douglas M. Jamba discloses the use of a dosimetry cup to collect charges impacting a target during ion beam implantation. To more accurately measure the charge actually impacting the target, a biasing electrode located between a beam defining aperture and the entrance to the cup is used to suppress electrons and negative ions that are trying to leave the cup. The biasing electrode also suppresses electrons generated on the defining aperture that are trying to enter the cup, and repels electrons that are carried with the ion beam.
A paper entitled "High Current Dosimetry Techniques" copyright 1979 by C. M. McKenna discloses use of one or more dosimetry cups located adjacent to the target for in-situ measurements of the charge bombarding the target during ion beam implantation. Measurements made by such dosimetry cups are used to control the ion beam being used for implantation. McKenna further discloses a negatively biased cup collector surface used in conjunction with less negatively biased cup walls to repel unwanted electrons from entering the cup. However, McKenna rejected the use of a negatively biased cup collector because experiments showed that this type of electrical biasing caused eruptions on the silicon target due to electrical discharges aggravated by secondary electrons trapped on the magnetic field lines within the dosimetry cup.